SLC SLC Testbed Proposal Testbed Proposal

Jeff GronbergJeff Gronberg

working groupworking group

SC Linear Collider RetreatSC Linear Collider Retreat

June 26 – 29, 2002June 26 – 29, 2002

The Basic Proposal

• Goal:– Generate and observe luminosity at SLC

• Requirements:– Revive the SLC, <$2M– Install laser and new beampipe– Run and observe e+e- in the SLD

calorimeter

Engineering Test Facility at SLC

Beam EnergyDRx,y (m-rad)

FFx,y (m-rad)

x / y

z

x,y

N

30 GeV

1100 / 50

8 / 0.1 mm

0.1 – 1.0 mm

1500/55nm

6.0E9

<$2M to revive the SLC

Photon Collider Testbed HardwareOptical Assembly

• Unknown factor: Optics damage– IP cannot often be opened up to fix the optics

• Radiation damage to the coating• Laser power damage to the mirrors

– What is the MTBF?

½ scale version of the NLC designPosition of final quads in SLC sets the scale

Final focus optics are fixedSteering mirrors are on piezo movers

Wavefront quality is the key determinant of laser power

• Only the laser light on-axis matters

• A good wavefront allows a diffraction limited spot to be achieved

• Laser power required (spot size)2

• With low quality optics the round trip through the optics reduces on-axis intensity 1/3

• Low quality optics (/30), $20K

• Good quality optics (/100), $200K

Photon Collider Testbed HardwareBeampipe

• Initial design of a beampipe has been done– New beampipe must be plug replaceable with the old

– Can this be done before demounting the old beampipe?

– Other IP hardware in this region that must be integrated?

• New quads or old?– Can the old quads accommodate light pipe?

– The old setup may not have any wiggle room.

Photon Collider Testbed HardwareAlignment System

• Similar systems in use– ½ Scale prototype of optics / alignment system is

currently under construction– Operation in end of FY02– Demonstration of alignment tolerances

Photon Collider Testbed Hardware Beamsplitter

• Single laser pulse is converted into 2 and time delayed– 2 ½ power lasers are twice as expensive as 1 full power laser

– Similar to, but much simpler than the splitter needed for NLC

• Laser power required 0.1 Joules x 2 at the IP– Assume losses and wavefront degradation, choose laser pulse 0.5

– Laser power 0.5 x 30 Hz = 15 Watts

Experimental program

• Pulse-to-pulse conversion measurement– Electrons that have interacted are off-energy

• They will be lost in the extraction line

– Measure the bunch charge before the IP and just before reaching the beam dump

– Collect data on the stability and consistency of the laser light delivered to the conversion point

• Direct luminosity measurement– e+e-– The SLD calorimeter will be revived in order to

observe this process

2 2 processes in SLC

• Tohru Takahashi spent March at LLNL– Compared calculations of 2

2 processes in GRACE, CompHEP and pandora

– Analyzed angular dependance of final states and the importance of the Calorimeter for this measurement.

– Determined required running times for a reasonable measurement.

Comparison of CAIN with a simple PANDORA parameterization

Kinematic separation of , e, ee

• The three possible scatters can be separated solely with their kinematic information– Identify two hit events

in the calorimeter

– No tracking required

ee

e

ee

w/ acolinearity cut

Angular Distributions

• The three diagram calculators give similar results

• is peaked forward much less strongly than ee

• Full calorimetric coverage in angle will greatly improve the counting rate

Spent beam in the final focus

• David Asner interfaces the CAIN particle output to the particle tracking code MAD

– Will off-energy particles hit the superconducting quads?

– For single Compton scatters the energy spread is 20-30 GeV/c

– Multiple scatters worsen the low energy straggling

• Seryi provides a simulation deck for the current beam line

– No hits for the current SLC – configuration

– However, at full laser power there is considerable beam loss

– Magnet quench is the limiting factor.

Allowable conversion rate at SLC- is limited by the need to minimize multiple Compton backscatters.

Outstanding issues

• Tunnel radiation simulation– Particle losses are known, contact radiation group at SLAC for

limits and remediation

• Installation plan– The old beam pipe surely needs to come out and be measured

before we will be ready to begin construction on the new– Otherwise, laser installation should be orthogonal

• Run plan– Mainly a question of the luminosity delivered and how long it will

take to make a measurement in the Calorimeter

• Costing– Should be driven by achieving the best luminosity/cost ratio

• Maximize bunch charge• FF improvements useful?